A lot of studies have heretofore been made, relating to PSQ. Baney et al's general review shows a ladder structure, a completely-condensed structure, an incompletely-condensed structure and an amorphous structure, as the structure of PSQ of which the existence has been confirmed (Reference 1). The completely-condensed structure is a structure in which plural cyclic structures form closed spaces and the shape of the closed spaces is not defined. The incompletely-condensed structure differs from the completely-condensed structure in that at least one site of the latter is not closed and the space thereof is not closed.
Feher, et al. obtained an incompletely-condensed structure PSQ by hydrolyzing cyclopentyltrichlorosilane or cyclohexyltrichlorosilane in acetone (Reference 2). Shchegolikhinea, et al. obtained a cyclic tetramer PSQ having a terminal of Si—O—Na, by hydrolyzing phenyltributoxysilane with an equimolar amount of sodium hydroxide and an equimolar amount of water in butanol (Reference 3).
However, there has been reported no example of synthesizing PSQ having a completely-condensed or incompletely-condensed structure according to the Shchegolikhinea et al's method. Of PSQ having a completely-condensed or incompletely-condensed structure, there are not so many types of compounds that have been easily synthesized and isolated. Of those, the number of commercially-available ones is further limited. Recently, PSQ derivatives produced by introducing various functional groups into PSQ having a completely-condensed or incompletely-condensed structure have been put on the market by Hybrid Plastics, and various applications have been proposed from them (Reference 4).    Reference 1: Chem. Rev. 95, 1409 (1995),    Reference 2: Organometallics, 10, 2526 (1991),    Reference 3: Organometallics, 19, 1077 (2000),    Reference 4: POSS CHEMICAL CATALOG, Hybrid Plastics (February 2001).
However, there are known only a few types of basic backbones of commercially-available PSQ derivatives, including organosilicon groups except a bonding state represented by SiO3/2. Accordingly, in order to effectively utilize PSQ derivatives having a completely-condensed structure or an incompletely-condensed structure in broad applications, it is desired to provide a PSQ derivative having a novel backbone structure. It is also important that the derivative can be produced within a shorter period of time at lower costs than conventional ones. Further, already-existing PSQ derivatives have another problem in that they are not compatible with general organic polymers. They could not be uniformly mixed with polymers; and when they are in coating films, they may whiten the films or they may bleed out of the films. Accordingly, their amount to be added is limited. For these reasons, some PSQ could not satisfactorily impart the characteristics expected of PSQ to polymers. Therefore, in order to broaden the applicability of PSQ, the compatibility thereof with general organic polymers must be improved. To solve the problems with the conventional PSQ derivatives, the present invention provides a novel PSQ derivative and a method for producing it within a short period of time at low costs.